Recent studies from our laboratory have implied that pulmonary microsomes may be important in the outcome of hyperoxic cellular damage. With the reduction of microsomal hemoproteins (cytochrome P-450) through the action of interferon inducers, there was a marked improvement of the survival of rats in hyperoxia. Using isolated microsomes, we found that H2O2 generation increased in hyperoxic environments as reported by others. Moreover, in the presence of added P450 substrates, H2O2 production increased even more with hyperoxia, supporting our view that cytochrome P450 was central to the generation of oxygen radicals in hyperoxia. Since in vivo the pulmonary microsome is expected to encounter both endogenous and exogenous P450 substrates, hyperoxic experiments using P450 substrates promises to be an important new avenue to pursue. Thus, in our subsequent experiments, when microsomal hemoprotein content (P450) and activity of cytochrome P450 were reduced by using interferon inducers, the production of H2O2 from pulmonary microsomes in the presence of hyperoxia and P450 substrates was reduced significantly. Our preliminary studies, however, are not conclusive. Thus, the major thrust of this proposal is to define the role of pulmonary microsomal cytochrome P450 system in hyperoxia. The degree of damages will be judged by the changes of endogenous microsomal components as well as exogenously administered deoxyribose (Project IA). The role of cytochrome P450 in causing damages will be evaluated by taking advantage of the "enhancers" of oxygen radical generation from cytochrome P450, for example certain P450 substrates and "inhibitors" such as carbon monoxide (Project IB, IC, ID). Once the role of cytochrome P450 in normal microsomes in hyperoxia is defined, we will examine the consequences of reduced quantities of cytochrome P450 through the use of interferon and interferon-inducers in reducing microsomal damages under hyperoxic conditions (Project IE). Similar strategies will then be applied to the study of type II cells and endothelial cells in culture (Project II). Here we will examine the changes of the microsomal damaging capabilities through the use of P450 substrates and interferon, in the natural environment of the endoplasmic reticulum. Our proposed study of pulmonary microsomes is but an initial entry into this complex and important field of intracellular free radical pathology.